Covariation in population trends and demography reveals targets for conservation action

Abstract

Wildlife conservation policies directed at common and widespread, but declining, species are difficult to design and implement effectively, as multiple environmental changes are likely to contribute to population declines. Conservation actions ultimately aim to influence demographic rates, but targeting actions towards feasible improvements in these is challenging in widespread species with ranges that encompass a wide range of environmental conditions. Across Europe, sharp declines in the abundance of migratory landbirds have driven international calls for action, but actions that could feasibly contribute to population recovery have yet to be identified. Targeted actions to improve conditions on poor-quality sites could be an effective approach, but only if local conditions consistently influence local demography and hence population trends. Using long-term measures of abundance and demography of breeding birds at survey sites across Europe, we show that co-occurring species with differing migration behaviours have similar directions of local population trends and magnitudes of productivity, but not survival rates. Targeted actions to boost local productivity within Europe, alongside large-scale (non-targeted) environmental protection across non-breeding ranges, could therefore help address the urgent need to halt migrant landbird declines. Such demographic routes to recovery are likely to be increasingly needed to address global wildlife declines.

Keywords: conservation; demography; migration; population trends; productivity.

Figure 1.

Mean site-level trends in abundance between 1994 and 2013 (a–c), mean standardized site-level productivity between 2004 and 2014 (d–f), and mean standardized site-level annual survival rates between 2004 and 2014 (g–i) of resident (a,d,g), arid-zone migrant (b,e,h), and humid-zone migrant (c,f,i) bird species breeding on 13 859 PECBMS sites (a–c), and 336 Euro-CES sites (d–i) across Europe. (Online version in colour.)

Figure 2.

Covariation between resident bird species and their co-occurring arid-zone (a,c,e), and humid-zone (b,d,f) migrant species in mean site-level (a,b) population trends (a: 12 103 sites; b: 13 267 sites), (c,d) standardized mean site-level productivity (c: 156 sites; d: 247 sites), and (e,f) standardized mean site-level annual survival rates (e: 156 sites; f: 247 sites). Lines of best fit are shown for significant associations and numbers indicate the number of sites. Horizontal bars indicate medians, boxes indicate interquartile range, whiskers indicate minimum and maximum values and circles indicate values 1.5 times higher or lower than 1st and 3rd interquartile, respectively. (Online version in colour.)